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Compression Springs

A compression spring

Compression springs are the most common type of spring used in the engineering industry. They are open coiled springs which are relatively easy to design and manufacture.

Compression springs can be made from round or square wire, although round is considerably cheaper and easier to manufacture. We keep a vast selection of material sizes and types in stock, from standard spring steels to nickel alloys, all of which can be used to manufacture compression springs.

The performance of a compression spring depends on the following factors:

Wire size - Increasing the wire size of a compression spring will make the spring stronger. We stock all the standard wire sizes and also a large range of non-standard wire sizes for specific requirements. A list of standard sizes is given in our technical help section here.

Diameter - As the diameter of the spring increases the strength (rate) will decrease. Also, when a compression spring is compressed the diameter will increase slightly. To avoid the spring jamming, if the spring is to work over a rod or inside a hole, specify the size of rod or the hole it is to go into.

Number of coils - The number of active coils is inversely proportional to the rate of a compression spring. This means a large number of coils will result in a fairly weak spring and a small number of coils will give a relatively strong spring. The total coils is dependant on the type of end given to the spring (see below). Springs with closed or closed and ground ends will usually have one inactive coil at each end.

Length - It is usual to specify the free length required. The solid length (fully compressed length) can easily be calculated or, if required, the working length for a specified load.

Rate - The rate (strength) of the spring depends on all of the above factors and can easily be calculated. However, sometimes the rate is the starting point from which the design can be based. This is particularly useful if the forces at particular working lengths are critical. Rate is defined as the force that has to be applied to the spring in order to produce a unit deflection, and is measured in either Newtons per mm (N/mm) or pounds per inch (lb/in).

End types - There are three basic types of end finish for compression springs:

Open ends.

Closed ends, not ground.

comp_ecg.gif (20869 bytes)

Ends open,
and not ground.
Ends closed,
and not ground.
Ends closed
and ground (ECG).

The most common type of end finish is the closed and ground end which is the most stable type as it provides a much greater area for the spring to exert it's force onto.

Hand - This is the direction in which the coils are wound (clockwise or anticlockwise) and is illustrated in these diagrams. It is actually quite obvious what hand a spring is once you learn to recognise it: A Right-Hand wound spring is like a corkscrew and would screw down when twisted clockwise, a Left-Hand wound spring is the opposite.

Index - This is the ratio of the mean diameter to the wire diameter. A low index indicates a tightly wound spring (a relatively large wire size wound around a relatively small diameter mandrel giving a high rate). The British Standard for compression springs (BS1726 part 1) does not give tolerances for springs whose index is less than 3.5 or greater than 16 but even so, a spring should ideally have an index of between 5 and 10.

Stresses - When a compression spring is compressed the active coils are stressed in torsion. There is a physical limit to the torsional stress that any material can withstand and it is this maximum stress limit which constrains the maximum force which can be obtained from a spring. It is an easy for our design programs to calculate these stress levels for your spring ensuring that the spring performs well during use. For more information contact our design department.

Spring Nests - In certain situations it is often necessary to incorporate a nest of springs where one spring is placed inside another. This is of particular use where space is limited such as engine valve springs. Again, if you require further information please contact our design department.

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